The present invention relates to a wheel hub clutch assembly adapted for use in a four-wheel drive vehicle, and more particularly to a wheel hub clutch assembly for automatically effecting engagement between a drive axle and a wheel hub in response to rotation of the drive axle.
One of such wheel hub clutch assemblies as described above has been proposed in U.S. Pat. No. 4,281,749 issued on Aug. 4, 1981. As is illustrated in FIG. 9, the wheel hub clutch assembly comprises a cylindrical body C integrally formed therein with a first set of clutch teeth C.sub.1 and secured to the outer end B.sub.1 of a wheel hub B rotatable on a stationary axle tube A, a sleeve member E fixedly mounted on the outer end of a drive axle D rotatable in axle tube A for rotation therewith, a clutch member F integrally formed with a second set of clutch teeth F.sub.1 to be engaged with the first clutch teeth C.sub.1 and axially slidably mounted on the sleeve member E for rotation therewith, cam means G operatively coupled with the outer end of axle tube A and rotatable relative to the sleeve member E during rotation of the drive axle D, cam follower means H axially slidably mounted on the sleeve member E for rotation therewith and cooperable with the cam means G to be displaced toward the clutch member F in response to rotation of the drive axle, a connecting member J engaged with the cam follower means H and the clutch member F to permit relatively inward movement between the cam follower means H and the clutch member F, and a spring retainer K secured to the outer end of the drive axle D. The clutch assembly further comprises a first coil spring L interposed between the outer end of connecting member J and the retainer K for biasing the clutch member F inwardly for movement away from engagement with the first clutch teeth C.sub.1, and a second coil spring M interposed between the cam follower means H and the clutch member F for biasing the clutch member F outwardly for movement toward engagement with the first clutch teeth C.sub.1. With such an arrangement, the movable clutch member F is subjected to a preload by the second coil spring M during rotation of the drive axle. As a result, it is advantageous that in the even clutch engagement is blocked in response to rotation of the drive axle, slight relative rotation between the clutch teeth under the preload relieves the blockage to effect smooth clutch engagement. However, the wheel hub clutch assembly is constructed large in its axial length due to the arrangement of the first and second coil springs L and M in series. For this reason, there is a problem that such a conventional wheel hub clutch assembly may not be mounted within a confined space at the outer end of the drive axle D.